Microbial nutrition and growth
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LECTURES IN MICROBIOLOGY. Microbial Nutrition and Growth. Sofronio Agustin Professor. LESSON 5. Lesson 5 Topics. Microbial Nutrition Environmental Factors Microbial Growth. Microbial Nutrition. Based on intake: (a) Macronutrients (CHONPS) (b) Micronutrients (trace elements)

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Microbial Nutrition and Growth

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Microbial Nutrition and Growth

Sofronio Agustin



Lesson 5 Topics

  • Microbial Nutrition

  • Environmental Factors

  • Microbial Growth

Microbial Nutrition

  • Based on intake:

    (a)Macronutrients (CHONPS) (b)Micronutrients (trace elements)

  • Based on carbon content:

    (a)Organicnutrients- contain carbon

    (b)Inorganicnutrients- simple atom or molecule without carbon

Chemical Composition

Bacteria are composed of different elements and molecules, with water (70%) and proteins (15%) being the most abundant.

Essential Nutrients

  • Carbon source

  • Energy Source

  • Growth Factors

Carbon Source

  • Autotrophs - obtain carbon from inorganic molecules like CO2

  • Heterotrophs - obtain carbon from organic matter from other life forms

    (e.g. sugar, proteins and lipids)

Energy Source

  • Photoautotrophs and photoheterotrophs obtain energy from sunlight

  • Chemoautotrophs derive electron energy from reduced inorganic compounds

  • Chemoheterotrophs obtain electron energy from hydrogen atoms of organic compounds

Nutritional Categories

Summary of different nutritional categories of microbes based energy and carbon sources


  • Methanogens are chemoautotrophic microbes

  • Example: methane producing Archaea

Extracellular Digestion

Cell Membrane

  • Phospholipid bilayer with integral and peripheral proteins

  • “Fluid mosaic” model - phospholipids and proteins move laterally

  • Exhibits “selective permeability”

Membrane Transport

  • Passive:

  • Simple diffusion

  • Facilitated diffusion

  • Osmosis

  • Active:

  • Permease

  • Group translocation

  • Endocytosis

Simple Diffusion

  • Net movement of solute from area of high concentration to a low concentrated area

  • No energy is expended

  • Down the concentration gradient (like a river flowing downstream)


A cube of sugar will diffuse from a concentrated area into a more dilute region, until an equilibrium is reached.

Facilitated Diffusion

  • Transport of polar molecules and ions across the membrane down their concentration gradients

  • No energy is expended (passive)

  • Carrier protein facilitates the binding and transport




Facilitated Diffusion

Facilitated Diffusion: The Process


  • Diffusion of solvent (usually, water) through a permeable but selective membrane

  • Water tends to move toward higher solute concentrated areas


Fate of cells in different osmotic conditions - isotonic, hypotonic, and hypertonic solutions

Active Transport

  • Transport of molecules against its concentration gradient

  • Requires energy and transport protein

    (Ex. Permeases and protein pumps transport sugars, amino acids, organic acids, phosphates and metal ions)

  • Group translocation transports and modifies specific sugars


  • Large substances are taken in by the cell but are not transported through the membrane.

  • Requires energy (active)

  • Common in eukaryotes

    - Phagocytosis

    - Pinocytosis

Active Transport

Example of permease, group translocation and endocytosis

Cellular Transport : Summary

Environmental Factors

  • Temperature

  • Gas

  • pH

  • Osmotic pressure

  • Other factors

  • Microbial association


  • Psychrophiles – (cold loving) 0 to 15 °C

  • Psychrotrophs - (food spoilage) grow between 20 to 30 °C

  • Mesophiles- (most human pathogens)

    20 to 40 °C

  • Thermophiles- (heat loving) 45 to 80 °C

  • Themoduric - (contaminants of heated food) survive in short exposures to high temp

  • Hyperthermophiles - (Archaea)

Temperature Tolerance

Gas Requirements

  • Two gases that influence microbial growth:


    • Respiration - terminal electron acceptor

    • Oxidizing agent - toxic forms

      (2)Carbon dioxide

Oxygen Metabolites

  • Superoxide radical - O2 -

  • Singlet oxygen - O2 with single electron in its valence shell

  • H2O2

    All are toxic byproducts of metabolism neutralized by enzymes SOD (superoxide dismutase), peroxidase and catalase.

Bacterial Types

  • Obligate aerobe

  • Facultative anaerobe

  • Obligate anaerobe

Obligate Aerobes

  • Require oxygen for metabolism

  • Possesses enzymes that can neutralize the toxic oxygen metabolites:

    SOD, peroxidase and catalase

  • Ex: Most fungi, protozoa, and bacteria like Bacillus sp. and Pseudomonas sp.

Obligate Anaerobes

  • Cannot use oxygen for metabolism

  • Do not possess SOD and catalase

  • The presence of oxygen is toxic to the cell

  • Ex: Clostridium sp. and Bacteroides sp.


Anaerobic culture techniques: (a) anaerobic chamber, (b) anaerobic jar

Facultative Anaerobes

  • Does not require oxygen for metabolism, but can grow in its presence

  • During minus oxygen states, anaerobic respiration or fermentation occurs

  • Possess superoxide dismutase and catalase

  • Ex. E. coli and S. aureus

Thioglycolate Broth

Thioglycollate broth is used to demonstrate aerotolerance of bacteria.

Aerobes, facultative anaerobes, and obligate anaerobes can be detected using this medium.

Other Gas Requirements

  • Microaerophiles - requires less than 10% of atmospheric O2.

    Ex: Campylobacter jejuni

  • Capnophiles - requires increased CO2 (5-15%) tension for initial growth.

    Ex: S. pneumoniae


  • Most cells grow best between pH 6-8

  • Acidophiles (up to pH 0) - molds and yeast

  • Alkalinophiles (up pH 10) urea-decomposing bacteria like Proteus sp.

Osmotic Pressure

  • Osmophiles - live in solutions with high solute concentration (e.g. sugar content in jams)

  • Halophiles - requires high salt concentrations and

    withstands hypertonic conditions

    Ex. Halobacterium sp. (Archaea)

  • Facultative halophiles - can survive high salt conditions but is not required for survival

    Ex. Staphylococcus aureus

Other Factors

  • Radiation- withstand UV, infrared rays

  • Barophiles – withstand high pressures

  • Spores and cysts- can survive dry habitats

Microbial Interactions

Influence microorganisms have on other microbes:

  • Symbiotic relationship

  • Non-symbiotic relationship

Symbiotic Relationship

Organisms that live together in close nutritional relationships


  • Mutualism – both organism benefit

  • Commensalism – only one organisms benefits

  • Parasitism – typically host-microbe relationship


  • “Satellitism”

    as a form of commensalism

  • Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae, which grows around colonies of S. aureus.

Non-Symbiotic Relationships

  • Organisms are free-living, and do not rely on each other for survival

  • Types:

    • Synergism – shared metabolism enhances growth of both microbes

    • Antagonism- competition between microorganisms

Microbe-Host Interactions

  • Can be commensal, parasitic, and synergistic

  • Ex. E. coli produce vitamin K for the host

Microbial Growth

  • Binary fission

  • Generation time

  • Growth curve

  • Enumeration of bacteria

Binary Fission

  • Parent cell enlarges and duplicates its DNA

  • Septum formation divides the cell into two separate chambers

  • Complete division results in two identical daughter cells

Steps in Binary Fission

Rod-shaped bacteria undergoing binary fission

Growth Curve

  • Lag phase

  • Log phase

  • Stationary phase

  • Death phase

Phases of Bacterial Growth

Growth curve in a bacterial culture.

Enumeration of Bacteria

  • Direct Methods:


    (b)Viable plate count

    (c)Membrane filtration

    (d)Most probable number

  • Indirect Methods:


    (b)Metabolic assay

    (c)Dry weight determinations

Direct Microscopic Count

  • The direct cell method counts the total dead and live cells in a special microscopic slide containing a premeasured grid.

  • Petroff-Hausser counting chamber used in dairy industry.

Standard Plate Count

Serially diluted samples are plated out and bacterial count expressed in CFU/ml.

Membrane Filtration

Membrane filtration and coliform counts.


Turbidimetric measurements as indicators of bacterial growth.

The greater the turbidity the larger the population density.

Coulter Counter

  • The Coulter Counter uses an electronic sensor to detect and count the number of cells.

  • Rapid automated counting method

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